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Moon and Saturn

Geysers of liquid water squirt into space from cracks in the ice near the south pole of Enceladus, one of the moons of Saturn, in this recent image from the Cassini spacecraft. They form bright streaks from the bottom of the moon, which is hovering above the bright limb of Saturn. Some scientists think the geysers are powered by a "Perrier" ocean of fizzy bubbles. [NASA/JPL/SSI]

[audio: opening bottle; fizziness]

People are popping a lot of bottle tops this week, releasing a lot of fizzy bubbles into the air.

The same process may be taking place on one of the moons of Saturn. In this case, the fizziness comes not from a bottle, but from a "Perrier" ocean beneath the moon's icy crust.

Enceladus is an intriguing little moon. Its surface is the most reflective in the solar system -- it's almost pure white. But the region around the south pole is marred by a series of cracks, known as tiger stripes. These cracks are hundreds of degrees warmer than the surrounding terrain. More important, though, geysers squirt water through the cracks and out into space.

Scientists have devised several models to explain the geysers. One says that they erupt from a global ocean that's rich in minerals and bubbles of gas -- hence the comparison to Perrier.

The model says that the bubbles force their way up through the tiger stripes, carrying some of the water with them. As they near the surface, the bubbles pop, spewing out water, gas, and minerals. Some of the material falls back to Enceladus, creating fresh ice. But some escapes into space, adding fresh ice to one of Saturn's rings.

Saturn is in good view near our own moon late tonight. They rise after midnight, and stand high in the south at first light, with Saturn to the upper left of the Moon. The star Spica is nearby, too; more about that tomorrow.

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